Figure 3.

Rhodopsin phosphorylation by GRK1. (A) Deactivation of rhodopsin is under control of a Ca²⁺-feedback loop involving Ca²⁺-sensor proteins recoverin and calmodulin. Both Ca²⁺-binding proteins have non-overlapping binding sites in GRK1 and act in a synergetic mode, for example by increasing the Ca²⁺-sensitivity of GRK1 regulation. (B) Inhibition of GRK1 is relieved at decreasing Ca²⁺-concentration after illumination leading to phosphorylation of rhodopsin. Structures were prepared with pymol; corresponding PDB codes are: 1F88 for rhodopsin (Palczewski et al., 2000); 3C51 for GRK1 (Singh et al., 2008); 1JSA for recoverin (Ames et al., 1997); 1CDM for calmodulin (Meador et al., 1993).